About determining reliable etching rates and the role of temperature in kinetic experiments on acidic wet chemical etching of silicon

Abstract

A characteristic of the wet chemical etching of silicon in concentrated HF-HNO3 and HF-HNO3-H2SiF6 mixtures is the release of a high reaction heat, without its numerical value being known. This...

Kinetic studies on acidic wet chemical etching of silicon in binary and ternary mixtures of HF, HNO3 and H2SiF6

“…Contrary to eqn (1), this process is not independent of the oxidation by nitric acid or the N(III) intermediate. Thus, an excess of the reactive N(III) species HNO 2 , which is indicated by a characteristic blue coloration of the etching mixture 7,9 caused by the dissolved N 2 O 3 present in the equilibrium, on the one hand results in the acceleration of the reaction 7,8,19 and on the other hand also in the suppression of hydrogen formation. 1 This reaction process and its stoichiometry, as well as the reaction rate, are sensitively affected by the reaction conditions, primarily the amount of etching mixture provided to dissolve the Si.…”

“…1 This reaction process and its stoichiometry, as well as the reaction rate, are sensitively affected by the reaction conditions, primarily the amount of etching mixture provided to dissolve the Si. 1,2,19 Consequently, the absence of H 2 formation throughout the complete mixing range (HF/HNO 3 ) and the exorbitantly high etching rates in the work of Robbins and Schwartz 3 can be explained retrospectively by using insufficient amounts of etching mixture in relation to the amount of dissolved silicon. 19 In addition, there is a disproportionately high heating of small amounts of etching mixture caused by the high exothermicity of the reaction process enthalpy of about À750 kJ mol À1 , which leads to the ''self-acceleration'' of the reaction.…”

“…1,2,19 Consequently, the absence of H 2 formation throughout the complete mixing range (HF/HNO 3 ) and the exorbitantly high etching rates in the work of Robbins and Schwartz 3 can be explained retrospectively by using insufficient amounts of etching mixture in relation to the amount of dissolved silicon. 19 In addition, there is a disproportionately high heating of small amounts of etching mixture caused by the high exothermicity of the reaction process enthalpy of about À750 kJ mol À1 , which leads to the ''self-acceleration'' of the reaction. 19 Simultaneously, with increasing reaction temperature, the conversion of NO with undiccociated HNO 3 in the side reaction increases, 2 while the stability of N 2 O 3 or the reactive species HNO 2 decreases.…”

“…19 In addition, there is a disproportionately high heating of small amounts of etching mixture caused by the high exothermicity of the reaction process enthalpy of about À750 kJ mol À1 , which leads to the ''self-acceleration'' of the reaction. 19 Simultaneously, with increasing reaction temperature, the conversion of NO with undiccociated HNO 3 in the side reaction increases, 2 while the stability of N 2 O 3 or the reactive species HNO 2 decreases. 7 Previous kinetic investigations into the HF/HNO 3 etching system are often limited to studies on the temperature dependence of the etching rate and thus to the determination of activation energies.…”

“…In particular, these are surface effects, such as increased etching rates of sawn and thus latticestrained surfaces, 23,40,41 or the consideration of the reaction time of accumulation of reactive species, 7,8,37 declared as the induction phase and subtracted from the reaction time, by subjective evaluation criteria. 23,41 In contrast, the newly developed method for determining the reaction rate in the bulk silicon under quasi-stationary reaction conditions and at precisely defined reaction temperatures 19 allows a more accurate and unbiased view of the formal kinetics of silicon etching in binary and ternary etching mixtures of HF, HNO 3 and H 2 SiF 6 . The focus of the present investigations is on the construction of formal kinetic models that are valid for an extensive range of composition of the etching mixtures.…”